The present invention relates to an external storage device using a non-volatile semiconductor memory and, more particularly, to access control on the non-volatile semiconductor memory.
As an external storage device using a non-volatile semiconductor memory, there is an external storage device using a flash memory. An example of the external storage device using a flash memory is described in Japanese Patent Laid-Open No. 27924/1993, “EXTERNAL STORAGE SYSTEM USING SEMICONDUCTOR MEMORY AND CONTROL METHOD FOR THE SAME”. In the external storage device using a flash memory, sector data is written to an area accessible to the user of the flash memory (hereinafter referred to as the user data area) in accordance with a write command issued by a host computer. In addition, the sector data stored in the user data area is read in accordance with a read command issued by the host computer. The writing and the reading of the sector data are performed for the entire user data area.
In the standard “ANSI X3.279-1996 AT Attachment Interface with Extensions”, access to user data is restricted by a security function using a password.
The above related arts provide the security of access to the whole of the user data area, but do not restrict access to individual sector data stored in the user data area. In addition, the related arts provide protection for the whole of the user data area, but do not take account of protection for a specified area of the user data area.
If no protection for a specified area of the user data area is provided, in a host computer using an external storage device, all user data areas are protected or are not protected, therefore the ease of use of the external storage device is degraded. In addition, protection for all user data areas imposes restrictions on a protection method for user data in the host computer, and such a restriction becomes a problem to the degree of freedom of the system design of the host computer and the external storage device.